Lotus Elan

Tuning

PostPost by: bobm3142 » Fri Aug 19, 2011 9:11 am

I feel guilty not have put in the time to probe the problem for myself: the response from everyone is awesome. I have had a look (just for half an hour) and can say that the rear carb is running rich. The No.1 plug was correct colour, No.2 was alittle black [loose carbon], No.3 was blacker and No.4 much thicker black coating [loose]. The plugs are clearly all new with a gap of 0.070". It's definately electronic ignition so a large gap is OK. Next job is to try to find a strobe light (I used to have one many, many moons ago so it might still be here). I'll follow up a contact you guys gave me before I set about adjusting the mixture of the rear carb. Actually, I now think that the fault is also present at higher revs but not really noticeable. It is not present with gentle acceleration or steady running.

I'll kep you posted.

Regards,

Bob
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PostPost by: bobm3142 » Fri Aug 19, 2011 9:37 am

nebogipfel wrote:Hello Bob, Welcome to the forum and to ownership of one of the best cars in the world.

FYI Miles Wilkins is in your neck of the woods..... http://fibreglassservices.com/index.html He wrote the book on the Lotus twincam (literally :D )

There are some clever chaps on this forum but FWIW my approach would be to go back to basics and check things in a methodical fashion. I always start with sparks and then go on to fuel.



I have just spoken to Miles and he deffinately knows Lotus cars. He is extremely helpful and is happy to look at my Elan to tell me exactly what I have got under the bonnet and sort my problem. He is well aware of my problem and says that above 2800rpm it will be fine and just a simple adjustment to put it right below thsi speed. I'll take my car to him next month and I will let you guys know the technical detail.

Once again many thanks for all your help.

Cheers,

Bob
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PostPost by: iancockshull » Fri Aug 19, 2011 7:15 pm

Bob

Have you got the original airbox with the engine breather connected to the airbox backplate, near No. 4 carb? (assuming Weber or Del Orto). The black soot on No4 plug might be coming from oil mist being burnt in the rear cylinder.

Best regards
Ian
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PostPost by: bobm3142 » Sun Aug 21, 2011 3:30 pm

iancockshull wrote:Bob

Have you got the original airbox with the engine breather connected to the airbox backplate, near No. 4 carb? (assuming Weber or Del Orto). The black soot on No4 plug might be coming from oil mist being burnt in the rear cylinder.

Best regards
Ian



Hi Ian,

No it's not the original box. The black soot is deffinately from too much petrol and not oil burning; oil and petrol leave quite different types of deposite. Thanks for the thought and message.

Regards,

Bob
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PostPost by: hatman » Mon Aug 22, 2011 8:25 am

bobm3142 wrote: The plugs are clearly all new with a gap of 0.070". It's definately electronic ignition so a large gap is OK.



Really? That wide? :shock: (My own, admittedly limited, understanding is that after-fitment of electronic ignition enables an increase in plug gap of the order of 5 thou, not 50 thou. Even modern engines designed with in-built electronic systems only run gaps around the 40 thou mark from my experience.)
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PostPost by: bobm3142 » Mon Aug 22, 2011 9:40 am

hatman wrote:
bobm3142 wrote: The plugs are clearly all new with a gap of 0.070". It's definately electronic ignition so a large gap is OK.



Really? That wide? :shock: (My own, admittedly limited, understanding is that after-fitment of electronic ignition enables an increase in plug gap of the order of 5 thou, not 50 thou. Even modern engines designed with in-built electronic systems only run gaps around the 40 thou mark from my experience.)


Hi, Yes I do agree that the gap is larger than I would expect. From playing arround with old electronic ignitions [many years ago] I formed a view that if the spark was strong enough to jump the gap then a large gap was best. I was have expecting to see a gap in the order of 0.040 to 0.050 but I don't know the characteristics of the plugs I've got so am quite happy to leave the gap as set, for the moment at least. As an aside, I have known a car to work perfectly well with 0.090 gap but that was with Capacitive discharge rather than the usual inductive discharge; the capacitave discharge systems have a very, very much more powerful spark [plugs don't last long though]. Actuall a second thought, since its really easy to do I think I'll try reducing the gap to 0.045 and see if it makes any difference. What I don't want to do is upset the running at 3000+ revs because this is realy good (recent rolling road test gave 122bhp @ 6000rpm).

Many thanks for your input,

Regards,

Bob
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PostPost by: VDB 50K » Wed Oct 12, 2011 10:51 am

bobm3142 wrote:
UAB807F wrote:
bobm3142 wrote:
sounds like a problem i had with my sprint,which also had aldon's module fitted.check,with a very good timing light,one that can measure advance in degrees,that it advances correctly.aldon set initial timing at 10 degrees ,not 12 as stated in manual.the advance is mechanical and cannot be altered,it should be 14 degrees(max) at 2,500 revs,this is why you need a good quality timing light.all details as said previousl are in the manual. my dizzy,after strip down,had only one return spring...sent it back to aldon who repaired it and it made a hell of difference....good luck.

I don't know much about Weber carbs but I'll locate the accelerator pump to see if I can clean the jet(s) without altering the other settings. I know that they do work (to some extent at least) since: a) the acceloration is good at high revs and, b) I use a couple of pumps prior to a cold engine start (and too many pumps or on a hot engine and it floods all too easily). Thanks for your help. Bob

The pump jets are within the carb body and it is fairly significant dismantling to get to them. From what you say about starting then it sounds like at least some of the 4 are working as when mine have been stuck the car has been very difficult to start.

Roughly what is the rev range that this "feature" happens over ? I recall several road testers commented on a flat spot just after tickover and I wonder if this could be the problem you're experiencing. My first thoughts would be to work through the electrics starting with the ignition timing at tick over and a couple of spots in the rev range (the settings are in the manuals for every 1000rpm). If that looks strange, it might be worth checking distributor advance weight are free to move & not stuck.

If you don't have a manual yet (and you really, really, really do need a proper Lotus one) then I dare say a PM to most forum members would get you the relevant page posted :wink:

Brian


Thanks for the reply, Brian. It runs well at any revs including tick-over, but from tickover up to about 2000 rpm it dies if I don't accelerate gently. It might be that the acceleration at higher revs will improve too if I sort this problem (wow! is all I can say to that). I am going to start from the state of the plugs and work my way through the ignition and then ignition timiing. It has electronic ignition so I have yet to work out how the auto advance and retard. works. Modern electronic ignition sorts the whole thing out but mine might still rely on the distributor for the auto advance.

The response has been anazing. Thanks guys I'll let you know how I get on.

Cheers,

Bob
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PostPost by: Foxie » Wed Oct 12, 2011 6:44 pm

types26/36 wrote:Welcome Bob,
Before getting too involved with tuning and by the way you describe the problem I would first check that the accelerator pumps are working and/or the pump jets are not blocked.

And the first thing I would do before dismantling anything is to operate the throttle while looking into the venturis. You should see a nice strong squirt in each barrel :D
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PostPost by: bill308 » Wed Oct 12, 2011 9:44 pm

Hi Bob.

By all means, ensure your ignition is operating as it should as a prerequisite for follow on tuning.

I think your plug gaps are way too wide. Unless you're trying to run a very lean mixture, I don't think there is any value in running gaps larger than 0.030-0.040 inches. Running a larger than necessary gap requires the ignition to produce a higher voltage to bridge the gap.

The other thing to pay attention to and to improve off idle performance, is to carefully balance the carb air flows. Balance in important up to about 2000 rpm and makes a big difference in low end torque and driveablility. It's also important in being able to set the mixtures correctly. I have found that a cylinder that is not flowing a minimum amount of air, will not respond to mixture adjustments.

Best of luck,
Bill
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PostPost by: bobm3142 » Fri Nov 11, 2011 10:12 pm

Hi Bill,
Thanks for your advice.

My Elan has been at the menders for quite a while now having some body works done and the water pump replaced., plus a few other bits too. However, they did not improve the problem discussed. They said that it would need significant money throwing at the carbs to address it. But I know that they haven't tried anything other than re-installing them following the water pump replacement.

I'll check that the accelerator pump jets are not blocked and that the pumps work to some extent by watching for petrol with these jets removed (one at a time), then I'll check that the air flows seem equal (by either a hose to my ear or if that doesn't seem viable when I try, I'll make an air flow animonitor (spelling?) ). I'll then adjust the mixture screws since the car is running too rich. Oh yes! the garage have set the plug gaps to 0.025" since they missed the fact that it is electronis ignition so I'll increase them to 0.030".

Many, many thanks for youe input.

Regards,

Bob
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PostPost by: UAB807F » Sat Nov 12, 2011 6:15 am

Hi Bob,

If you are checking air flows through the individual chokes, then I use a gunsons carbalancer kit. It's basically a length of tubing with a variable intake at one end and a manometer at the other. It looks and is quite a cheap piece of kit, but I've found it works remarkably well and makes it very easy to set the chokes to the same air flow. It probably takes longer to pull off the air box cover and replace it afterwards than it does to set the chokes up using the kit.

Brian

ps - no affiliation to the seller, but this is the type of thing

http://www.amazon.co.uk/Gunson-G4053-Carbalancer/dp/B002WN0TT0/ref=sr_1_1?ie=UTF8&qid=1321078167&sr=8-1
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PostPost by: bobm3142 » Mon Nov 14, 2011 10:24 am

Hi Brian,

Thanks for the info. It is very timely since I'm contemplating whether to set the carbs myself (I have no equipment) or pay to have it done (not very conveniet to take the car and wait, at the mement though). They appear to really need adjusting. Despite getting the car in August I have had very little time to look at it. I had work done on the engine and body and have only just got it back. What I have just found (last night) is that the static ignition timing was set to about 8 deg AFTER TDC! I have now set this to 10 Before TDC and it runs so much better. It has electronic ignition and I could only check the timing by looking for the spark, as I rotated the engine, and observing where the timing mark, on the pulley, was. Also I played with the mixture screws, just to see if it made much difference (the new plugs were obviously BLACK with rich fuel burning after only a few miles) and found that the front carb was far, far too rich and that turning the screws on the rear carb made no difference at all, even if I closed them completely. Hence, I believe that the air flows to the carbs are well out of balance. Didn't have time (and too dark) to take the air intake off to listen to the air flows.

Once again many thanks for your help.

Regards,

Bob
UAB807F wrote:Hi Bob,

If you are checking air flows through the individual chokes, then I use a gunsons carbalancer kit. It's basically a length of tubing with a variable intake at one end and a manometer at the other. It looks and is quite a cheap piece of kit, but I've found it works remarkably well and makes it very easy to set the chokes to the same air flow. It probably takes longer to pull off the air box cover and replace it afterwards than it does to set the chokes up using the kit.

Brian

ps - no affiliation to the seller, but this is the type of thing

http://www.amazon.co.uk/Gunson-G4053-Carbalancer/dp/B002WN0TT0/ref=sr_1_1?ie=UTF8&qid=1321078167&sr=8-1
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PostPost by: Spyder fan » Mon Nov 14, 2011 8:46 pm

Bob,
Something that is often overlooked on the pump jets is the tiny aluminium washers that are used as a seal. Go back to Brians post with the pictures of the carburettor and the location of the pump jets, you can just make out the shiny silver of the washer on the jet in the last picture. Sometimes these washers are missed off completely in a so called rebuild and can also be flattened or damaged by over tightening.

When I still had a twincam with webers in my car I had your problem with no pickup from low rev's and a set of new washers on the pump jets cured it.

See this exploded diagram for details, it's item 49 (washer) and fits to item 57 (pump jet)http://petrolpowered.com/include/pages/tech/spitfire/images/diagrams/dcoe45.png

You can buy them here, http://www.ebay.co.uk/itm/WEBER-DCOE-PUMP-JET-ALLOY-WASHERS-SET-4-NEW-/200647679021possibly the best ?3.60 you will spend in a long time.
Kindest regards

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PostPost by: bobm3142 » Mon Nov 14, 2011 10:43 pm

types26/36 wrote:Welcome Bob,
Before getting too involved with tuning and by the way you describe the problem I would first check that the accelerator pumps are working and/or the pump jets are not blocked.



Hi,

I have removed each of the 4 pump jets and they are all totally clean and blockage free. I have also observed that petrol is pumped very freely when the accelorator linkage is moved, with these jets removed.

I have also observed that the idle rpm was governed by the front carb accelorator stop screw adjustment and when I increased that on the rear carb, so that it was just dictating the idle rpm, then the mixture screws on the rear carb started to have an effect. I have now roughly adjusted all 4 mixture screws but not jet driven the car to see what improvement it has made. I have yet to look at the balance of the two carbs. Perhaps I'll purchase the vacuum gauge arrangement you stated; it's quite cheap (low cost).

Thanks once again.

Bob
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PostPost by: bobm3142 » Mon Nov 14, 2011 10:48 pm

Spyder fan wrote:Bob,
Something that is often overlooked on the pump jets is the tiny aluminium washers that are used as a seal. Go back to Brians post with the pictures of the carburettor and the location of the pump jets, you can just make out the shiny silver of the washer on the jet in the last picture. Sometimes these washers are missed off completely in a so called rebuild and can also be flattened or damaged by over tightening.

When I still had a twincam with webers in my car I had your problem with no pickup from low rev's and a set of new washers on the pump jets cured it.

See this exploded diagram for details, it's item 49 (washer) and fits to item 57 (pump jet)http://petrolpowered.com/include/pages/tech/spitfire/images/diagrams/dcoe45.png

You can buy them here, http://www.ebay.co.uk/itm/WEBER-DCOE-PUMP-JET-ALLOY-WASHERS-SET-4-NEW-/200647679021possibly the best ?3.60 you will spend in a long time.



Hi,

Brilliant info, many thanks. I'll have a look to see if the small washers are there and replace them any way in case they are damaged.

Regards,

Bob
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